Resurgence of Pertussis -- United States, 1993

From January 3 through December 4, 1993 (weeks 1-48), 5457 pertussis cases were reported to CDC -- an 82% increase over the number reported during the same period in 1992 (3004) and the highest annual number of cases reported since 1967 (Figure_1). Compared with 1992, the number of reported pertussis cases increased in 35 states, especially those in the New England, middle-Atlantic, North Central, and Mountain regions (Figure_2). During 1993, large outbreaks have occurred in Chicago and Cincinnati. This report summarizes epidemiologic characteristics of pertussis cases reported through December 4, 1993. Characteristics

Of 4989 persons with pertussis for whom age was known, 2218 (44.4%) were infants (i.e., aged less than 1 year); 1031 (20.7%), aged 1-4 years; 563 (11.3%), aged 5-9 years; and 1177 (23.6%), aged greater than or equal to 10 years. Of 1976 infants for whom age in months was reported, 1555 (78.7%) were aged less than 6 months and 421 (21.3%), aged 6-11 months. Vaccination Status and Complications

Supplemental reports about vaccination status and complications were available for 744 (13.6%) cases. Of 596 persons for whom vaccination status was known, 368 (61.7%) had received fewer than three doses of diphtheria and tetanus toxoids and pertussis vaccine (DTP) *. Of 207 children aged 7 months-4 years who were "age-eligible" to have received three doses of DTP, 33 (15.9%) had received no doses, and 97 (46.9%) had received fewer than three doses. Of infants with pertussis for whom data on disease severity were available, 212 (65.2%) of 325 had been hospitalized, 45 (15.8%) of 285 had had pneumonia confirmed radiographically, and five (1.6%) of 305 had had seizures resulting from pertussis. Of the 5457 persons with pertussis, seven died. Outbreaks

Chicago. From July 1 through October 30, a total of 226 persons with suspected cases of pertussis were reported to the Chicago Department of Health. Of these, 70 (31.0%) persons tested culture-positive for Bordetella pertussis; an additional 96 (42.5%) persons met the CDC clinical case definition for pertussis ** during outbreaks. Of the remaining 60 cases, 29 (48.3%) did not meet the clinical case definition, and 31 (51.7%) are still under investigation. Of the 166 persons whose illness met the case definition or who had culture-confirmed pertussis, the median age was 9 months (range: less than 1 month-35 years). Most (127 {76.5%}) of these cases were reported by a single pediatric teaching hospital, and 70 (42.2%) persons were hospitalized (median hospital stay: 5 days). Of 111 persons aged greater than 2 months with pertussis for whom previous vaccination history was available, 52 (46.8%) were not up-to-date with DTP vaccinations. Of 61 persons with pertussis aged 7 months-4 years, 30 (49.2%) had received fewer than three doses of DTP, and six (10.0%) had received no doses.

Cincinnati. From July 1 through October 30, a total of 285 suspected cases of pertussis were reported to the Cincinnati Health Department: 164 (57.5%) cases were culture-confirmed; 102 (35.8%) occurred in infants. Nearly all (265 {93.0%}) cases were reported by a single large teaching hospital, and 95 (33.3%) persons were hospitalized. Measures to control this epidemic included introduction of an accelerated DTP vaccination schedule (doses given at 1, 2, and 3 months of age) for infants. Investigation of this outbreak is ongoing. Reported by: J Wilhelm, MD, T Kenyon, MD, E Mihalek, K Brusealas, Chicago Dept of Health; S Shulman, MD, E Bergman, Children's Memorial Hospital, Chicago; R Daum, MD, Wyler Children's Hospital, Chicago; BJ Francis, MD, State Epidemiologist, D Robinson, Illinois Dept of Public Health. M Adcock, PhD, J Daniels, MD, V Wells, MD, Cincinnati Health Dept; C Christie, MD, S Reising, PhD, Children's Hospital Medical Center, Cincinnati; TJ Halpin, MD, State Epidemiologist, Ohio Dept of Health. R Finger, MD, State Epidemiologist, Dept of Health Svcs, Kentucky Cabinet for Human Resources. National Immunization Program, CDC.

Editorial Note

Editorial Note: Based on the number of pertussis cases reported through December 4, the projected total number of cases for 1993 will be the highest reported since 1967. Since 1976 (when the lowest number of pertussis cases {1010} was reported), the number of reported cases in peak years has steadily increased (Figure_1); in 1990 (the last peak year), 4570 cases were reported. Despite the recent resurgence in pertussis, the number of cases reported in 1993 represents a more than 96% decline from the annual number reported during the prevaccine era (i.e., before 1948).

Complications associated with pertussis may be severe, especially among infants. Rates of complications among infants during 1993 have been similar to those reported during 1980-1989, when 69% were hospitalized, 22% developed pneumonia, 3% had seizures, 1% had pertussis encephalopathy, and 0.6% died (2). The two groups currently at greatest risk for severe complications are infants aged less than 6 months (the age by which children are recommended to have received three doses of DTP) and preschool-aged children who are undervaccinated. The finding that approximately 50% of preschool-aged children with pertussis in 1993 were undervaccinated underscores the importance of timely vaccination of children according to the recommendations of the Advisory Committee on Immunization Practices (ACIP) ***. During outbreaks involving primarily young infants, introduction of an accelerated DTP vaccination schedule (doses given at ages 6, 10, and 14 weeks) should be considered; for preschool-aged children, receipt of three or more doses is highly protective against severe disease caused by pertussis (4).

Pertussis incidence is usually characterized by a cyclical pattern, with peaks occurring at 3- to 4-year intervals; the increase in reported cases in 1993 coincides with the expected cyclical peak. However, the total number of reported cases has increased in each successive peak year since 1977 (Figure_1); reasons for this resurgence of pertussis are unclear. Vaccination coverage with three or more doses of DTP among children aged 2 years has remained relatively stable but low (approximately 70%) since 1962 (CDC, unpublished data). Furthermore, the proportion of reported pertussis cases among children aged 1-4 years has not increased during 1980-1993. These observations suggest that the recent increase in pertussis incidence is related neither to a decrease in vaccination coverage nor to a substantive reduction in DTP vaccine efficacy.

As the incidence of pertussis has increased, the proportion of reported cases among persons aged greater than or equal to 10 years has increased -- from 15.1% during 1977-1979 to 19.8% during 1980- 1989 and 26.9% during 1992-1993. Adolescents and young adults play an important role in transmitting pertussis to susceptible infants because vaccination-induced immunity to pertussis wanes with increasing age (beginning approximately 4 years after the last dose) (5-8). In addition, pertussis among adolescents and adults is often atypical and is frequently not diagnosed (9).

In addition to prevention through vaccination, control of pertussis and interruption of transmission requires prompt recognition of disease by health-care providers and timely administration of effective antimicrobials (i.e., erythromycin or trimethoprim-sulfamethoxazole) to persons with pertussis and their close contacts (8). Health-care providers should consider the diagnosis of pertussis in persons of all age groups who develop a cough lasting more than 7 days. Because only 10% of pertussis cases are reported (10), surveillance must be enhanced. In addition, all cases should be investigated promptly. In the future, introduction of new acellular pertussis vaccines for use in adolescents or young adults may potentially reduce the disease burden in these age groups and among young children.

References

1. Medical Research Council. The prevention of whooping cough by vaccination. Brit M J 1951;1:1463-71.

2. Farizo KM, Cochi SL, Zell ER, Brink EW, Wassilak SG, Patriarca PA. Epidemiological features of pertussis in the United States, 1980-1989. Clin Infect Dis 1992;14:708-19.

3. ACIP. Diphtheria, tetanus, and pertussis: recommendations for vaccine use and other preventive measures -- recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-10).

4. Onorato I, Wassilak SG, Meade B. Efficacy of whole-cell pertussis vaccine in preschool children in the United States. JAMA 1992;267:2745-9.

5. Lambert HJ. Epidemiology of a small pertussis outbreak in Kent County, Michigan. Public Health Rep 1965;80:365-9.

6. Jenkinson D. Duration of effectiveness of pertussis vaccine: evidence from a 10-year community study. BMJ 1988;296:612-4.

7. Bass JW, Stephenson SR. The return of pertussis. Pediatr Infect Dis J 1987;6:141-4.

8. Biellik RJ, Patriarca PA, Mullen JR, et al. Risk factors for community- and household-acquired pertussis during a large-scale outbreak in central Wisconsin. J Infect Dis 1988;157:1134-41.

9. Herwaldt LA. Pertussis in adults: what physicians need to know. Arch Intern Med 1991;151:1510-2. 

10. Sutter RW, Cochi SL. Pertussis hospitalizations and mortality in the United States, 1985-1988: evaluation of the completeness of national reporting. JAMA 1992;267:386-91.

* Three doses of DTP is the minimum number required for effective protection against pertussis (1).

** Cough illness lasting greater than or equal to 14 days without other apparent cause. 

*** DTP at ages 2, 4, 6, and 15 months, with an additional dose at age 4 6 years (3). Diphtheria and tetanus toxoids and acellular pertussis (DTaP) vaccine may be used for the fourth and fifth doses in the series, beginning at 15 months of age.
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